Such a ladder is disclosed in U.S. Pat. No. 5,117,943. The cable mechanism used in this ladder makes it possible, by means of a simple, manual operation of the cable line, to release the locking of the ladder elements, to both extend and also retract the extendable ladder on the base ladder, and to subsequently again securely lock the reciprocal position of the ladder elements. In particular, when a telescopic change of the ladder must be carried out often, such an easily handled locking is very effective and time saving. The locking bracket, which is intended for a locking of this type, is pivotal by means of the cable line and is fastened on the extendable ladder. The locking bracket is thereby created in such a manner so as to be pivotable into the area of the base ladder such that it will rest on the next lower rung after the cable line operation has ended, and can only again be pivoted out of this position reciprocally locking the ladder elements after the extendable ladder has been slightly lifted against the force of gravity. The locking bracket is formed in such a manner that it subsequently, with the extendable ladder lifted, is pivoted by the rungs of the base ladder during passing without the cable line having to be operated; and after a brief subsequent return the locking bracket lockingly pivots or swings back. If the extendable ladder is instead supposed to be lowered on the base ladder, then the cable line is, also after a short lift, operated until the desired retraction of the extendable ladder is reached, which is thereafter further lowered until the locking bracket, as described, rests on the next rung of the base ladder. Aside from the advantages of such a ladder adjustable through a cable line, the known arrangement, however, has a relatively complicated design of the individual structural elements, which makes the manufacture of such a ladder unnecessarily more expensive. The multi-part locking bracket is pivotally supported on both sides on the spars by means of a special bearing block, which must each be screwed to one of the spars. Each of the utilized guide rollers is supported in a bearing housing, which has an eyelet in a bar extending over the cable, on which bar the bearing housing is pivotally suspended on the respective inner cheek of the adjacent spar. The known arrangement therefore requires many individual parts and a considerable amount of work during its installation on the ladder.